Synthetic lubricants test performance

Some fundamental aspects of tribochemistry of ZDDP have been investigated using an ultrahigh vacuum UHV analytical tribometer on chemisorbed films previously formed on a steel surface (Martin et al., 1996). The steel surface was immersed in a solution of ZDDP at a concentration of 2 wt.% in PAO synthetic lubricant base at 130°C for 24 hours. The chemistry of the treated steel surfaces was investigated by XPS and AES, and friction tests were carried out in UHV just after the analysis. At the end of the friction tests, AES microanalysis was performed both inside and outside the wear scar. The AES analysis showed that sulfide was present inside the wear scar and phosphorus was eliminated from the surface, presumably as wear debris. Summary data of the tribofilm composition after ZDDP degradation are presented in Table 4.1. 

When the need for improved performance outweighs restrictions on price and desire for availability which ordinarily dominate the procurement of lubricants, then the purview expands to include fluids that can be made by synthetic chemistry. Even if we restrict ourselves to those fluids that promise reasonable potential for usefulness, there are as many as 20 broad generic classes which can come under consideration, and within each class there may be 10 or more subclasses gradated according to some property such as viscosity or molecular weight. A comprehensive survey of all the synthetic fluids with potential for practical use would be a major undertaking. In this chapter, therefore, we shall restrict ourselves to the examination of those types of synthetic lubricants that have been tested well enough to establish their usefulness and their limitations. 

The criteria listed above are also used to judge petroleum oils therefore evaluating synthetic lubricants by these criteria tests whether they perform better than petroleum oils under the conditions required by service. 

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